Electrostatic sound producer



w. D. cRozu-:R 1,851,240

ELECTROSTATIC SOUND PRODUCER March 29, 1932.

Filed Nov. 2. 1928 'Paie-nad ze, 1932 UNITED STATES PATENT OFFICE WILLIAI 1Dv OROZIEB, 0F GENEVA, ILLINOIS, ASSIGNOB, BY )im ASBIGNIEITI, TO 'UNITED BEPBODUGEBB PATENTS CORPORATION, 'OF ST. CHARLES, ILLINOIB A GOBPOBATION 0F NEVADA ELECTBOSTATIC BOUND PRODUCER application med november 2, ms. semi im.. autres.t

The present invention relates to electrostatic sound producers, such as are used in radioreception, although capable of use as a recorder as well as a reproducer.

. Among the objects of the invention is to rovide a novel sound producer having a 'electric under proper tension to produce the best sound results and to avoid foreign sounds. In the case of using a dielectric sheet of fabric type, if the threads be in the direction of tension, wrinkles will form in the cross threads, and there is no tension in the direction of these wrinkled cross threads. With such a condition and when the dielectric vibrates under the electrostatic stresses, foreign sound and noises are produced. To avoid this, the fabric is dis sed with the threads'on a bias or diagonal y to the direction of stress. This also aids in permitting the fabric to better flex under the impressed electrostatic stresses. Also changes in temperature willnot distort the fabric so that' unwanted sounds are avoided.

maintain the dielectric always under the proper tension irrespective of the amplitude of vibration of the dielectric. By such novel means and with the biasing of the dielectric elements, it is facile to stretch the dielectric sheet over the conducting surface of the conductor, and the stretching will be even.

When usin a rubberized fabric, such as rubberized si r, this invention allows a free stretching of the rubber constituent whereby betterelasticity is obtained for the dips in the troughs of the conducting plate under the electrostatic forces, whenv the plate is made with corrugations, or troughs or depressions.

The invention also comprehends a novel form of securing means for the dielectric.

-Other objects, capabilities advantages and features are comprehended by the invention as will later appear and as are inherently possessed thereby.

Referring to the drawings, Fig. 1 is a face view of an electrostatic sound producer constructed in accordance with the invention, with a part broken away to show the construction of the device;

Anate form of tensioning means;

Fig. 5 is a similarview showing a. novel form of securing means; and

Fig. 6 is a fragmentary sectional view showing a further alternate form of tensionin means. p

o eferring now more in detail to the drawings, the embodiments selected to illustrate the invention is shown in connection with a frame 1 which may be'made of suitable insulating material, such as wood, fibre, bakelite, or .the like, such frame having end pieces 2 and 3 and cross pieces 4 and 5 connected at their ends to the side pieces 6 and 7 shown 10 in dotted lines in Fi 1 of the drawings.

The top of the ame is curved or convexed and supports a curved or convexed metal plate 8, which is lpreferably 'provided with corrugations 'or undulations and a plurality of openings or slots 9. The edge portions of the plate may have anges 10 fitting into rabbets 11 formed 'in the end and side pieces of the frame. Likewise, the plate may also have ianges 12 and 13 extending into and fitting lin rabbets formed in the cross pieces 4 and 5, as clearly shown in Fig. 2 of the drawings. c

Upon the plate S is stretched a dielectric sheet 14 which in the particular embodiment selected to illustrate the invention, is silk or rubberized silk. Upon the outer surface of the sheet 14 is provided a metallic coating, film or surface 15, such as gold leaf, tin foil, ormetallized surface medium for the fabric. W This dielectric -14l and the coating 15 thereon has its edge portion extendin over the flanges of the plate and into rab ts formed in the frame 1 and secured thereto in any v suitable manner, such 'as by tacks or the like 5 Whether conducting or non-conducting. When of conducting material, it may serve as a lead element contacting with the conducting coating on the dielectric. This tensioning bar is connected by a wire 19 extending into the space 17 and secured to the end of a spring 20, which has its other end connected to a cross pin 21 secured and passing through the cross members 4 and 5, as clearly shown in Fig. 2 of the drawings. The spring 20 imposes a tension on the bar 18, which in turn imposes a tension upon the dielectric 14 and coating 15 so as to depress a part 22 of the dielectricfabric into the upper part of the channel 17, as clearly shown in F i0. 2 of the drawings.

When the dielectric is of fabric type, which is preferable, the fabric is disposed so that it will have its threads 23 and 24 on a bias or diagonally of the line of pull or tension of the tension member 18. Fig. 1 shows the diagonal disposition of the threads with reference to the bar 18. When assembling the device, the dielectric sheet may be stretched over the plate 18 and the edges secured by the securing'elements 16 on three sides of each end portion of the frame. The tension means 18 will act upon the fourth side of each half of the sheet, and by reason of the biasing of the threads in the fabric, the tension will be evenly distributed and the fabric will not wrinkle, as Well as having the fabric under the desired tension determined upon the strength of the spring 20 used. In operation, the electrostatic forces act upon the dielectric to make thel same vibrate by attracting vand repelling the same with reference to the rigid plate 8. When the dielectric is attracted, it liexes into the corrugations or depressions and when it is repelled, it is caused to move in the opposite direction. The apertures or slots 9 provide for ready release of the pressure or rarefaction of the air between the dielectric and the plate 8.

Referring to Fig. 3, instead of attaching the fabric to the end ieces of the frame, the edge portions of the abric are attached to a tension member 25 by any suitable securing element 26. The tension member 25 is carried upon the ends of resilient members 27,

4rsuch as spring wire, or the like. The other end of the element 27 being secured in a suitable manner to the cross member 2 or 3 as the case may be. The spring 27 will impose a constant lateral pull against the tension member 25 and maintain the dielectric under tension in the same manner as the member 18 (in Fig- 2) will maintain the fabric under tension at the middle of th'.` device rather than at the end.

Fig. 4 is somewhat similar to Fig. 3, and has a tension member 28 to which the edge portion of the fabric is secured by suitable elements 29. From one of the securing elements 29 is connected a spring 30 which has an end connected to a pin 31'secured to the cross member 2. The spring 30 constantly urges the tension member 28 downwardly, and inasmuch as the fabric is extended around a curved portion* of the member 28 there is a constant pull or tension on the fabricto maintain the same in proper stretched and tensioned condition.

In Fig. 5 instead of using a frame, the metal plate has a flange portion 32 in which is provided a channel or oove 33 into which a rtion 34 of the marginal or edge portion o the fabric may extend. A securin element 35 in the form of a bar, rod or wire, is pressed into the channel 33 with the interposed curved portion 34 of the fabric, so as to hold and maintain the fabric in place. Any form of tensioning means, such as that shown in Figs. 1, 2 and 6 may be used to tension the fabric extending over the surface of the plate. The securing element ma be, if desired, of insulating material, suc ias wood, fibre, bakelite or other suitable maferial.

In Fig. 6 is shown a tension means comprising a member 18 with which is connected a wire 19 having its end connected to a leaf sprin 36 extending from and secured to a side ange 37 of the late 38. In this case the late 38 and the anges are integral and no ame is used as in the case of the forms shown in Figs. 1 and 2. The leaf spring 36 constantly urges a pull on the wire 19 and also on the tension member 18 so as to depress a part of the fabric into the space between the angeportion 39 and 40 of the plate 38, and hence maintain a constant and even tension on the fabric covering the plate 38.

While I have herein described and upon the drawings shown illustrative embodiments of the invention, it is to be understood that the invention is not limited thereto but may comprehend other constructions, arrangements of parts, details and features without de arting from the spirit thereof.

aving thus disclosed the invention, I claim:

1. An electrostatic sound producer comprising a ri 'd member having a conductin surface, a dlelectric sheet stretched over sai surface, said member having a channel, said dielectric sheet extending into said channel, and securing means in sald channel for holding the sheet in lace, a surface of said dielectr1c having con ucting material. y

2. An electrostatic sound producer comprising a rigid member having a conductin surface, a dielectric sheet stretched over sai surface, said member having a channel, said dielectric sheet extending into said channel, and a rod-like securing e ementkin said channel for hold the sheet in place, a surface of said dielectnchaving conduct' material.

3. An, electrostatic sound p ucer comlos prisin a rigid member having a conducting surface, a dielectric sheet stretched over said surface, said member having a channel, said dielectric sheet extending into said channel,

6 a rod-like securing element in said channel for holding the sheet in place, and tension means for holding the sheet in stretched condition, a surface of said dielectric having conducting material.

10 4. An electrostatic sound producer comprising a rigid member having a conducting surface, a dielectric sheet stretched over said surface, said member having a channel, said dielectric sheet extending into said channel,

and securing means in said channel for holdingthe sheet in place, and tension means for holding the sheet in stretched condition, a surface of said dielectric having conducting material.y A

In witness whereof, I hereunto subscribe my name to this speciiication.

WILLIAM D; CROZIER. 

